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Published November 28, 2017 | Supplemental Material
Journal Article Open

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush


Grafting density is an important structural parameter that exerts significant influences over the physical properties of architecturally complex polymers. In this report, the physical consequences of varying the grafting density (z) were studied in the context of block polymer self-assembly. Well-defined block polymers spanning the linear, comb, and bottlebrush regimes (0 ≤ z ≤ 1) were prepared via grafting-through ring-opening-metathesis polymerization. ω-Norbornenyl poly(D,L-lactide) and polystyrene macromonomers were copolymerized with discrete comonomers in different feed ratios, enabling precise control over both the grafting density and molecular weight. Small-angle X-ray scattering experiments demonstrate that these graft block polymers self-assemble into long-range-ordered lamellar structures. For 17 series of block polymers with variable z, the scaling of the lamellar period with the total backbone degree of polymerization (d* ∼ N_(bb)^α) was studied. The scaling exponent α monotonically decreases with decreasing z and exhibits an apparent transition at z ≈ 0.2, suggesting significant changes in the chain conformations. Comparison of two block polymer systems, one that is strongly segregated for all z(System I) and one that experiences weak segregation at low z (System II), indicates that the observed trends are primarily caused by the polymer architectures, not segregation effects. A model is proposed in which the characteristic ratio (C∞), a proxy for the backbone stiffness, scales with N_(bb) as a function of the grafting density: C∞ ∼ N_(bb)^(f(z)). The scaling behavior disclosed herein provides valuable insights into conformational changes with grafting density, thus introducing opportunities for block polymer and material design.

Additional Information

© 2017 American Chemical Society. Received: September 19, 2017; Accepted: October 26, 2017; Published: October 26, 2017. This work was supported by the Department of Energy under award number DE-AR0000683 (ARPA-E program) and by the National Science Foundation under award number CHE-1502616. A.B.C. thanks the U.S. Department of Defense for support through the NDSEG fellowship. This research used resources of the Advanced Photon Source, a U.S. Department of Energy Office of Science User Facility operated by Argonne National Laboratory under contract DE-AC02-06CH11357. The authors gratefully acknowledge M. A. Hillmyer, F. S. Bates, I. Haugan Smidt, M. J. Maher, and C. M. Bates for helpful discussions. The authors declare no competing financial interest.

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